Fig. 3: Dependence of cononsolvency on the polymer molecular weight.
From: A cosolvent surfactant mechanism affects polymer collapse in miscible good solvents
Schematic showing the dependence of the reversible work of cavity creation for the coil and globule states on the degree of polymerization N and its correlation to the LCST dependence in PNIPAM–water–methanol solutions46,47. The SASAs of both coil and globule states grow with increase in N due to which the methanol concentration required to saturate them also increases (green and yellow markers in the left panel). As the SASA of the coil state (\({{\rm{SASA}}}^{{\rm{C}}} \sim {N}^{{\alpha }_{{\rm{C}}}}\)) grows faster with N than that of the globule (\({{\rm{SASA}}}^{{\rm{G}}} \sim {N}^{{\alpha }_{{\rm{G}}}}\)) state, αC > αG, the difference between the rates of decrease in ΔGExcl−Vol for the coil and globule states rises with N (arrows in the left panel). These are the two aspects due to which the minimum in \(\Delta {G}_{{\rm{Excl}}-{\rm{V}}{\rm{ol}}}^{{\rm{C}}\to {\rm{G}}}\), and thereby the LCST, becomes deeper and shifts to higher methanol concentration with increase in N. The blue and red curves in the right panel represent the dependence of \(\Delta {G}_{{\rm{Excl}}-{\rm{V}}{\rm{ol}}}^{{\rm{C}}\to {\rm{G}}}\) (and LCST) on XMeOH for the two chain lengths on the left panel.
